Inductor for heating elongated metal workpieces

ABSTRACT

An inductor is provided having an axis of orientation which coincides with the axis of a metal workpiece disposed in magnetically coupled relationship therewith. The inductor is comprised of a continuous conductor including first and second helical portions which are diametrically opposed, extend about the axis of orientation, and are twisted to have the same hand of lay with respect to the axis of orientation.

United States Patent [1 1 I Lewis 1 Nov. 12, 1974 INDUCTOR FOR HEATINGELONGATED METAL WORKPIECES [75] Inventor: John C. Lewis, Wentworth,Ontario,

Canada [73] Assignee: Park-Ohio Industries, Inc.,

Cleveland, Ohio 221 Filed: Dec.26, 1973 21 App1.No.:428,413

[52] US. Cl 219/l0.79, 219/1057 [51] Int. Cl. H05b 5/08 [58] Field ofSearch 219/65, 10.79, 10.43,

219/10.57, 10.67, 10.73, 10.41; 266/4 El, 5 El [56] References CitedUNITED STATES PATENTS 3,203,211 8/1965 Mallinckrodt 219/65 X 3,271,1159/1966 Keller 219/1043 X Primary ExaminerBruce A. Reynolds [57] ABSTRACTAn inductor is provided having an axis of orientation which coincideswith the axis of a metal workpiece disposed in magnetically coupledrelationship therewith. The inductor is comprised of a continuousconductor including first and second helical portions which arediametrically opposed, extend about the axis of orientation, and aretwisted to have the same hand of lay with respect to the axis oforientation.

13 Claims, 7 Drawing Figures PATENTEB NOV 1 21974 SIIEUIOFZ FIG. 2

- PATENTELNUV] 2|974 SHEET 2 BF 2 INDUCTOR FOR HEATING ELONGATED METALWORKPIECES The present invention relates to the art of induction heatingand, more particularly, to an inductor for heating an elongated metalworkpiece.

It is well known in the art of induction heating to inductively heat ametal workpiece by means of an inductor in the fonn of a helical coilhaving an axis coinciding with the axis of the workpiece when the latteris disposed within the coil in magnetically coupled relationshiptherewith. Such a coil generally has a plurality of closely spacedconvolutions extending helically about the coil axis from one endthereof to the other, and the opposite ends of the coil areinterconnected with a source of power through which the coil isenergized. Upon energization of the coil, current flows along thehelical path defined by the convolutions, which path is substantiallytransverse to the direction of the coil axis, and a magnetic field isestablished between the coil and workpiece in the direction of the coilaxis to inductively heat the workpiece.

It is also known in the induction heating art to provide an inductorhaving parallel conductor portions extending longitudinally of the axisof the workpiece to be heated and generally along opposite sides of theworkpiece. With such inductors, current flows through the conductorportions parallel to the outer surface of a workpiece, whereby amagnetic field is established in a direction transverse to the workpieceaxis. Thus, those portions of the outer surface of the workpieceadjacent the longitudinally extending conductor portions are inductivelyheated and, in order to inductively heat the entire periphery of theworkpiece disposed within the confines of the inductor, either theworkpiece or the inductor must be rotated about its axis.

In the induction heating field, it is sometimes desirable to heatperipherally, at one time, a substantial axial portion or the entirelength of an elongated workpiece such as, for example, a rod, bar orthin walled metal tube. To heat simultaneously a given axial portion ofsuch a workpiece with a helical coil of the character mentioned above,requires of course that the coil have a length corresponding to thelength of the workpiece to be heated. The length of the workpiece to beheated may be several feet, whereby the use of a helical coil inductoris undesirable both from the standpoint of low heating efficiency andhigh coil cost.

To heat an elongated area of a workpiece employing an inductor havinginductor portions extending parallel to the workpiece axis provides forhigher heating efficiency and lower inductor cost, but requires relativerotation between the workpiece and inductor to achieve heating of theentire periphery of the workpiece. Special equipment is necessary toprovide for support of the workpiece in a manner which enables rotationthereof.

In accordance with the present invention, an inductor for heatingelongated workpieces is provided which has a geometry advantageouslyproviding for the peripheral surface of a workpiece to be heated along agiven longitudinal length thereof without the disadvantages attendant toheating such a workpiece with prior inductor configurations includingthose discussed hereinabove. More particularly, the inductor of thepresent invention advantageously provides for current flow to be in adirection longitudinally of the workpiece axis,

thus to increase heating efficiency and reduce the amount of conductormaterial required. At the same time, the inductor advantageouslyprovides for the workpiece to be heated peripherally in a manner whichis efficient with regard to heat disbribution and which does not requirerelative rotation between the workpiece and conductor portions of theinductor. Thus, the workpiece can be heated substantially uniformlyabout the periphery thereof in a minimum of time and without the specialapparatus required if the workpiece or inductor has to be rotated.

More particularly in accordance with the present invention, an inductoris provided having an axis coinciding with the axis of a workpiece whenthe latter is disposed in magnetically coupled relationship therewith,and the inductor includes conductor portions extending longitudinally ofthe axis of orientation and helically thereabout from one end of theinductor device to the other. The helical portions of the inductor aretwisted so as to have the same hand of lay with respect to the axis oforientation in a given longitudinal direction thereof. This geometryprovides for each of the helical conductor portions to extend, withrespect to a workpiece, from opposite sides thereof at a first locationprogressively along and laterally across the workpiece and thence topositions at a second location in which each conductor portion is on theside of the workpiece opposite that which it occupied at the firstlocation. Accordingly, current flows through the conductor portions in ahelical path extending longitudinally of the workpiece and progressivelyabout the periphery thereof so that peripheral areas of the workpiecedisposed within the inductor are simultaneously heated, as the workpieceprogresses through the inductor.

Either the inductor or the workpiece can be longitudinally displacedrelative to the other. In either case, the inductor geometry providesfor the length of the workpiece scanned to be uniformly heatedperipherally without relative rotation between the inductor andworkpiece.

Accordingly, an outstanding object of the present invention is theprovision of an inductor for heating elongated metal workpieces moreefficiently than heretofore possible.

Another object is the provision of an inductor for heating elongatedmetal workpieces peripherally thereof along a given axial length of theworkpiece in a manner which is more expeditious and efficient thanheretofore possible.

Yet another object is the provision of an inductor for heatinglongitudinal and peripheral areas of a workpiece and having conductorportions extending along helical paths having the same hand of lay in agiven longitudinal direction relative to the axis of the workpiece.

Still another object is the provision of an inductor for inductivelyheating an elongated workpiece of small dimension in cross section,which inductor has a length considerably greater than thecross-sectional dimension of the workpiece and which is comprised of aminimum amount of conductor material and achieves peripheral heating ofthe workpiece within the length of the inductor more efficiently andexpeditiously than heretofore possible in a progressive heatinginstallation.

The foregoing objects, and others, will in part be obvious and in partpointed out more fully hereinafter in conjunction with the descriptionof the drawings depicting preferred embodiments of the invention and inwhich:

FIG. 1 is a perspective view of an inductor made in accordance with thepresent invention;

FIG. 2 is a plan view of the inductor illustrated in FIG. 1;

FIG. 3 is an elevational view in cross section of the inductorillustrated in FIG. 1, the view beingalong line 33 in FIG. 1;

FIG. 4 is a perspective view of another embodiment of an inductor madein accordance with the present invention;

FIG. 5 is a sectional elevational view of the inductor illustrated inFIG. 4, the view being taken along line 55 in FIG. 4;

FIG. 6 is a perspective view of still another embodiment of an inductormade in accordance with the present invention; and,

FIG. 7 is a perspective view of yet another embodiment of an inductormade in accordance with the present invention.

Referring now in greater detail to the drawings wherein the showings arefor the purpose of illustrating preferred embodiments of the inventiononly and not for the purpose of limiting same, an inductor device isillustrated in FIG. 1 which is comprised of a continuous tabularconductor 10 of conductive material, such as copper. As illustrated,conductor 10 is in the form of a tube which is rectangular in crosssection and which has opposite ends 12 and 14. Ends 12 and 14 areadapted to be connected across a suitable source 16 of alternatingcurrent for energization of the inductor device. The tubular conductorprovides, in a well known manner, for cooling fluid, such as water, tobe circulated through the conductor to control the temperature thereofduring an induction heating operation. Accordingly, it will beappreciated that ends 12 and 14 of the conductor are adapted to beconnected to a source of cooling fluid, not illustrated.

The inductor device has an axis of orientation A which coincides withthe longitudinal axis of a workpiece W when the workpiece is disposed inmagnetically coupled relationship with the inductor so as to be heatedby the inductor upon energization thereof. Conductor 10 includes a leg18 extending longitudinally of axis A from end portion 12, a bridgingportion 20 extending across axis A from the outer end of leg 18, a leg22 extending longitudinally of axia A from bridging portion 20 to theopposite end of the inductor device, a bridging portion 24 extendingacross axis A from the corresponding end of leg 22, and a leg 26extending from the corresponding end of bridging portion 24longitudinally of axis A to end portion 14 of the conductor. It will beappreciated that the several legs and bridging portions may be integralwith one another or may be separate components suitably interconnectedsuch as by brazing.

As will be seen from FIGS. 1 and 2, leg 18 extends longitudinally fromend portion 12 and, with respect to the direction of bridging portion 24toward bridging portion 20, leg 18 is twisted counterclockwise 90. Leg22 extends longitudinally of axis A between the corresponding ends ofbridging portions 20 and 24 and, in the direction from bridging portion24 toward bridging portion 20, is twisted counterclockwise 180. Legportion 26 extends longitudinally of axis A between bridging portion 24and end portion 14 and, in the direction from bridging portion 24 towardbridging portion 20, is twisted counterclockwise It will be appreciated,therefore, that leg 22 defines a helical conductor portion and that legs18 and 26, together, define another helical conductor portion. Thehelical conductor portions extend longitudinally of axis A and, withrespect to the direction from bridging protion 24 toward bridgingportion 20, the two helical portions have the same hand of lay or, inother words, are twisted in the same direction relative to axis A.Preferably, the bending or twisting of legs 18, 22 and 26 is uniform,whereby the helical conductor portions at any given location along axisA and transverse thereof are diametrically opposed, as illustrated inFIG. 3.

Bridging portions 20 and 24 are provided, respectively, with openings 28and 30 coaxial with axis A for longitudinally receiving a workpiece W tobe heated. Openings 28 and 30, of course, are peripherally closed toenable coolant circulation through the inductor without leakage at theopenings. While openings 28 and 30 are illustrated as being circular itwill be appreciated that these openings can have other peripheralcontours. The diametrically opposed relationship between the helicalconductor portions provides for the rectangular tubular conductor legsto have their narrowest dimension extending radially with respect toaxis A and for the leg portions to lie in planes disposed on oppositesides of axis A and in parallel relationship. Preferably, the spacingbetween the helical conductor portions in the direction perpendicular tothe latter planes is substantially uniform throughout the length of theinductor device. The dimension of such spacing will depend in part onthe cross-sectional dimension of workpieces to be heated by theinductor, and the spacing will provide for the helical conductorportions to be suitably spaced from the outer surface of a workpiece. toachieve the desired magnetically coupled relationship between theinductor and workpiece.

It will be seen that the geometry of the inductor in FIGS. 1 and 2provides for current to flow through the helical conductor portionsalong a helical path and longitudinally of a workpiece positionedtherebetween. Accordingly, the magnetic field established between thehelical conductor portions and workpiece extends along a correspondinghelical path and has a direction along the path transverse to axis A.This advantageously provides for peripheral portions of workpiece W tobe substantially uniformly heated as the workpiece moves longitudinallyof the inductor and without having to rotate the workpiece relative tothe inductor. Such uniform heating is enhanced by providing for thetubular conductor to be rectangular in cross section and positioned suchthat its dimension in width is bisected by a line extending radially ofaxis A. This relationship provides for the magnetic field at any givenpoint along the length of the inductor to have a greater peripheralextent with respect to the workpiece than would be the case with asingle narrow conductor extending parallel to the workpiece axis. Thewidth dimension of the tubular conductor can of course vary and,preferably, is wider than the cross-sectional dimension of a workpieceto be heated.

While the tubular conductor illustrated in FIGS. 1 and 2 has a widthdimension which is flat, it will be appreciated that the conductor couldbe curved in cross section so as to be concave with respect to axis A.Such a configuration would be desirable for the heating of tubular orcircular workpieces in that the lateral side edges of the conductorwould be closer to the outer surface of the workpiece than the lateralside edges of the flat conductor.

In use, a workpiece to be heated may be introduced into the inductordevice from one of the opposite ends thereof and suitably supported formovement through the inductor and out the opposite ends. Alternatively,the workpiece may be of indeterminate length and progressively advancedthrough the inductor device for adjacent longitudinal portions of theworkpiece, or selected longitudinal portions thereof, to be heated.

Referring now to FIGS. 4 and 5 of the drawing, there is illustrated afurther embodiment of an inductor made in accordance with the presentinvention. The inductor in FIG. 4 is similar to the inductor in FIG. 1,but is defined by a continuous tubular conductor 40 of conductivematerial, such as copper, which is circular in cross section. Conductor40 has opposite ends 42 and 44 connectable across a suitable source ofalternating current 46, and the tubular conductor provides for thecirculation of coolant through the inductor. As in the embodiment ofFIG. 1, the inductor has an axis of orientation A coinciding with theaxis of workpiece W disposed in magnetically coupled relationshiptherewith.

Conductor 40 includes, in succession, a leg 48 extending from endportion 42, a bridging portion 50 extending across and under axis A fromthe corresponding end of leg 48, a leg 52 extending longitudinally ofaxis A from the corresponding end of bridging portion 50 to the oppositeend of the inductor, a bridging portion 54 extending across and overaxis A from the corresponding end of leg 52, a leg 56 extendinglongitudinally of axis A from the corresponding end of bridging portion54 to the opposite end of the inductor, a bridging portion 58 extendingacross and over axis A parallel to bridging portion 50, a leg 60extending longitudinally of axis A from the corresponding end ofbridging portion 58 to the opposite end of the inductor, a bridgingportion 62 extending across and under axis A parallel to bridgingportion 54, and a leg 64 extending longitudinally of axis from thecorresponding end of bridging portion 62 to end portion 44 of theconductor.

Legs 52 and 60 of the conductor together define one helical conductorportion, and leg 56 together with legs 48 and 64 define another helicalconductor portion. As in the embodiment of FIG. 1, each of the helicalconductor portions is twisted to have the same hand of lay relative to agiven longitudinal direction from one end of the inductor to the other.More particularly, in the direction from bridging portions 54 and 62toward bridging portions 50 and 58, the two helical conductor portionsare twisted counterclockwise relative to axis A. Preferably, the bendingor twisting of the two conductor portions is generally uniform betweenthe opposite ends of the inductor, and the conductor portions eachtraverse an angular path of 180 between the opposite ends of theinductor.

The adjacent legs of conductor 40 are maintained in suitable spacedrelationship by means of insulating spacers 66 disposed therebetween atspaced apart locations longitudinally of the inductor. Further, at anygiven location along the length of the inductor the helical conductorportions are substantially diametrically opposed as illustrated in FIG.5, and the axes of the conductor legs of each helical portion lie in aplane perpendicular to a line extending radially of axis A. Moreover,the conductor legs are spaced apart in the plane an equal distance onopposite sides of such a radial line.

As in the embodiment of FIG. I, the inductor geometry shown in FIG. 4provides for current to flow longitudinally relative to axis A along ahelical path, whereby the magnetic field extends along a correspondinghelical path and has a direction transverse to axis A.

Bridging portions 50 and 58 at one end of the inductor are suitablycontoured in the direction transverse to axis A to cooperatively providean opening 68 for a workpiece to be heated. Similarly, bridging portions54 and 62 at the opposite end of the inductor are contoured in thedirection transverse to axis A to provide an opening 70 for theworkpiece. Openings 68 and 70 preferably are coaxial with respect toaxis A and can be of a contour other than the circular contour shown.

In the embodiments illustrated in FIGS. 1 and 4, the opposite ends ofthe conductor are disposed intermediate the opposite ends of theinductor device. It will be appreciated, however, that many arrangementscan be provided for connecting the conductor to a source of alternatingcurrent without altering the intended operation of the inductor. Onesuch arrangement is illustrated in FIG. 6 wherein the inductor device iscomprised of a conductor formed of rectangular tubing similar to that ofconductor 10 illustrated in FIG. 1. In the present embodiment, conductor80 has opposite ends 82 and 84 disposed at one end of the inductor forinterconnection with a suitable source of alternating current 86. As inthe previous embodiments, the inductor has an axis of orientation Acoinciding with the axis of a workpiece W disposed in magneticallycoupled relationship therewith.

Conductor 80 includes one helical conductor portion 88 extendinglongitudinally of axis A from end portion 82 of the inductor to theopposite end of the inductor, a bridging portion 90 extending acrossaxis A at the corresponding end of helical portion 88, and a secondhelical conductor portion 92 extending longitudinally of axis A from thecorresponding end of bridging portion 90 to end portion 84 of theconductor. Helical conductor portions 88 and 92 are twisted to have thesame hand of lay in the direction from one end of the inductor to theother, in the manner described hereinabove with respect to theembodiments of FIGS. 1 and 4, and the bending or twisting provides forthe helical portions to transverse an angular path of 180 between theopposite ends thereof. Moreover, helical portions 88 and 92 are relatedto one another and to axis A so as to be diametrically opposed asdescribed hereinabove in connection with the embodiment of FIG. 1.Bridging portion 90 is porvided with an opening 94 coaxial with axis Ato receive a workpiece.

In FIG. 7 there is illustrated a further embodiment of an inductor madein accordance with the present invention. In this respect, the inductorhas an axis of orientation A adapted to coincide with the axis of aworkpiece W to be inductively heated. The inductor is comprised of aconductor in the form of a continuous hollow tube of conductive materialsuch as copper and which tube is circular in cross section. Conductor100 has opposite ends 102 and 104 adapted to be interconnected with asuitable source of alternating current 106. Conductor 100 furtherincludes a helical conductor leg 108 extending longitudinally of axis Afrom end portion 102 to the opposite end of the inductor, a bridgingportion 110 extending across and under axis A-from the corresponding endof helical leg 108, a helical conductor leg 112 extending longitudinallyof axis A from the corresponding end of bridging portion 102 to theopposite end of the inductor, a bridging portion 114 extending acrossand under axis A from the corresponding end of helical leg 112, ahelical conductor leg l16te the opposite ends of the inductor device. Itwill be appreciated, however, that many arrangements can be provided forconnecting the conductor to a source of alternating current withoutaltering the intended operation of the inductor. One such arrangement isillustrated in FIG. 6 wherein the inductor device is comprised of aconductor 80 formed of rectangular tubing similar to that of conductor10 illustrated in FIG. 1. In the present embodiment, conductor 80 hasopposite ends 82 and 84 disposed at one end of the inductor forinterconnection with a suitable source of alternating current 86. As inthe previous embodiments, the inductor has an axis of orientation Acoinciding with the axis of a workpiece W disposed in magneticallycoupled relationship therewith.

Conductor 80 includes one helical conductor portion 88 extendinglongitudinally of axis A from end portion 82 of the inductor to theopposite end of the inductor, a bridging portion 90 extending acrossaxis A at the corresponding end of helical portion 88, and a secondhelical conductor portion 92 extending longitudinally of axis A from thecorresponding end of bridging portion 90 to end portion 84 of theconductor. Helical conductor portions 88 and 92 are twisted to have thesame hand of lay in the direction from one end of the inductor to theother, in the manner described hereinabove with respect to theembodiments of FIGS. 1 and 4, and the bending or twisting provides forthe helical portions to transverse an angular path of 180 between theopposite ends thereof. Moreover, helical portions 88 and 92 are relatedto one another and to axis A so as to be diametrically opposed asdescribed hereinabove in connection with the embodiment of FIG. 1.Bridging portion 90 is porvided with an opening 94 coaxial with axis Ato receive a workpiece.

In FIG. 7 there is illustrated a further embodiment of an inductor madein accordance with the present invention. In this respect, the inductorhas an axis of orientation A adapted to coincide with the axis of aworkpiece W to be inductively heated. The inductor is comprised of aconductor 100 in the form of a continuous hollow tube of conductivematerial such as copper and which tube is circular in cross section.Conductor 100 has opposite ends 102 and 104 adapted to be interconnectedwith a suitable source of alternating current 106. Conductor 100 furtherincludes a helical conductor leg 108 extending longitudinally of axis Afrom end portion 102 to the opposite end of the inductor, a bridgingportion 110 extending across and under axis A from the corresponding endof helical leg 108, a helical conductor leg 112 extending longitudinallyof axis A from the corresponding end of bridging portion 102 to theopposite end of the inductor, a bridging portion 114 extending acrossand under axis A from the corresponding end of helical leg 112, ahelical conductor leg 116 extending longitudinally of axis A from thecorresponding end of bridging portion 114 to the other end of theinductor, a bridging portion 118 extending across and over axis A fromthe corresponding end of helical leg 116, and a helical conductor lcg120 extending longitudinally of axis A from the corresponding end ofbridging portion 118 to end portion 104 of the conductor at the oppositeend of the inductor.

Conductor legs 108 and 116 together define a helical conductor portionextending about axis A from one end of the inductor to the other, andconductor legs 112 and 1120 together define another helical conductorportion extending about axis A from one end of the inductor to theother. Bridging portions 110 and 118 are cooperatively contoured in thedirection transverse to axis A to provide a workpiece opening, andbridging portion 114 is contoured in the direction transverse to axis Aat the corresponding end of the inductor to enable the workpiece to beintroduced into the inductor in a manner similar to that describedhereinabove in conjunction with the previous embodiments. The helicalconductor portions are twisted to have the same hand of lay relative toaxis A in a direction from one end of the inductor device to the other.Moreover, each helical portion traverses an angular path about axis A ofbetween the opposite ends of the device, and the helical portions arediametrically opposed along the length of axis A and are geometricallyinterrelated with one another and with axis A in a manner describedhereinabove in connection with the inductor of FIGS. 4 and 5.

It will be appreciated that many embodiments of the present inventionmay be made and that many changes may be made in the embodiments hereindescribed without departing from the principles of the presentinvention. For example, where the inductor is defined by a continuousconductor of tubular material having a circular cross section, eachhelical conductor portion can be comprised of one or a number of tubularlegs other than the two legs described herein. Moreover, it will beappreciated that the cross-sectional contour of the conductor can beother than circular and can, for example, be polygonal. Further, it willbe appreciated that in those arrangements in which a conductor ofrectangular cross section is employed that the helical portions could bedefined by two or more rectangular conductor legs disposed side by siderather than one wide conductor leg. Accordingly, it is to be distinctlyunderstood that the foregoing descriptive matter is to be interpretedmerely as illustrative of the present invention and not as a limitation.

Having thus described my invention, I claim:

1. An inductor for inductively heating an elongated metal workpiecehaving an axis, said inductor having an axis of orientation coincidingwith the axis of a workpiece disposed in magnetically coupledrelationship therewith, said inductor comprising a continuous conductorhaving opposite ends connectable across a source of alternating current,and said conductor including first and second helical portions extendingabout said axis of orientation, said helical portions being of the samehand of lay and substantially diametrically opposed with respect to saidaxis of orientation.

2. The inductor according to claim 1, wherein said helical portions eachhave opposite ends longitudinally spaced apart and circumferentiallyspaced with respect to said axis of orientation.

3. The inductor according to claim 2, wherein each of said helicalportions traverses an angular path of 180 between said opposite ends.

4. The inductor according to claim 1, wherein said conductor is atubular conductor of rectangular cross section disposed with thesmallest dimension of said cross section extending in the direction ofsaid axis of orientation.

5. The inductor according to claim 4, wherein said first and secondhelical portions have corresponding first ends and said conductorfurther includes a bridging portion extending across said axis oforientation at said corresponding ends, said bridging portion having aworkpiece receiving opening therethrough coaxial with said axis oforientation.

6. The inductor according to claim 5, wherein said first and secondhelical portions have corresponding second ends and said conductorfurther includes a second bridging portion extending across said axis oforientation at said second ends, said second bridging portion having aworkpiece receiving opening therethrough coaxial with said axis oforientation.

7. The inductor according to claim 6, wherein said helical portions eachtraverse an angular path of 180 between the first and second endsthereof.

8. The inductor according to claim 7, wherein one of said first andsecond helical portions has terminal ends between said first and secondends thereof, said terminal ends defining said opposite ends of saidinductor.

9. The inductor according to claim 1, wherein said conductor is tubularin cross section, said helical portions of said conductor each includingat-least two portions of said tubular conductor disposed adjacent oneanother and generally parallel in the direction perpendicular to saidaxis of orientation.

10. The inductor according to claim 9, wherein said helical portionseach have opposite ends longitudinally spaced apart andcircumferentially spaced with respect to said axis of orientation.

11. The inductor according to claim 10, wherein each of said helicalportions traverses an angular path of between said opposite ends.

12. The inductor according to claim 11, wherein said tubular conductoris circular in cross section.

13. The inductor according to claim 9, wherein said first and secondhelical portions have corresponding opposite ends and said conductorfurther includes bridging portions extending across said axis oforientation at corresponding ones of said opposite ends, at least aportion of each of said bridging portions being spaced radially fromsaid axis of orientation a sufficient distance for said inductor toreceive a progressive workpiece.

1. An inductor for inductively heating an elongated metal workpiecehaving an axis, said inductor having an axis of orientation coincidingwith the axis of a workpiece disposed in magnetically coupledrelationship therewith, said inductor comprising a continuous conductorhaving opposite ends connectable across a source of alternating current,and said conductor including first and second helical portions extendingabout said axis of orientation, said helical portions being of the samehand of lay and substantially diametrically opposed with respect to saidaxis of orientation.
 2. The inductor according to claim 1, wherein saidhelical portions each have opposite ends longitudinally spaced apart andcircumferentially spaced with respect to said axis of orientation. 3.The inductor according to claim 2, wherein each of said helical portionstraverses an angular path of 180* between said opposite ends.
 4. Theinductor according to claim 1, wherein said conductor is a tubularconductor of rectangular cross section disposed with the smallestdimension of said cross section extending in the direction of said axisof orientation.
 5. The inductor according to claim 4, wherein said firstand second helical portions have corresponding first ends and saidconductor further includes a bridging portion extending across said axisof orientation at said corresponding ends, said bridging portion havinga workpiece receiving opening therethrough coaxial with said axis oforientation.
 6. The inductor according to claim 5, wherein said firstand second helical portions have corresponding second ends and saidconductor further includes a second bridging portion extending acrosssaid axis of orientation at said second ends, said second bridgingportion having a workpiece receiving opening therethrough coaxial withsaid axis of orientation.
 7. The inductor according to claim 6, whereinsaid helical portions each traverse an angular path of 180* between thefirst and second ends thereof.
 8. The inductor according to claim 7,wherein one of said first and second helical portions has terminal endsbetween said first and second ends thereof, said terminal ends definingsaid opposite ends of said inductor.
 9. The inductor according to claim1, wherein said conductor is tubular in cross section, said helicalportions of said conductor each including at least two portions of saidtubular conductor disposed adjacent one another and generally parallelin the direction perpendicular to said axis of orientation.
 10. Theinductor according to claim 9, wherein said helical portions each haveopposite ends longitudinally spaced apart and circumferentially spacedwith respect to said axis of orientation.
 11. The inductor according toclaim 10, wherein each of said helical portions traverses an angularpath of 180* between said opposite ends.
 12. The inductor according toclaim 11, wherein said tubular conductor is circular in cross section.13. The inductor according to claim 9, wherein said first and secondhelical portions have corresponding opposite ends and said conductorfurther includes bridgIng portions extending across said axis oforientation at corresponding ones of said opposite ends, at least aportion of each of said bridging portions being spaced radially fromsaid axis of orientation a sufficient distance for said inductor toreceive a progressive workpiece.